dmaengine: sh: rz-dmac: Use rz_dmac_disable_hw()

dmaengine: sh: rz-dmac: Use rz_dmac_disable_hw()

Use rz_dmac_disable_hw() instead of open coding it. This unifies the
code and prepares it for the addition of suspend to RAM and cyclic DMA.

The rz_dmac_disable_hw() from rz_dmac_chan_probe() was moved after
vchan_init() as it initializes the channel->vc.chan.device used in
rz_dmac_disable_hw().

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Tested-by: John Madieu <john.madieu.xa@bp.renesas.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Tested-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Link: https://patch.msgid.link/20260526084710.3491480-5-claudiu.beznea@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>